Since the invention of mode-locked lasers, considerable effort has been directed towards the generation of ultrashort optical pulses. Novel techniques for broad-band dispersion control now enable self-mode-locked Ti:Sapphire lasers to directly produce 6.5 femtosecond pulses. Compression of pulses down to sub-5 fs is achievable by treating the outputs of such lasers with novel spectral broadening techniques in external pulse compressors. Efficient pulse compression generally requires characterization of the pulses. Grating-pair or prism-pair compressors are commonly used to compensate mainly for second order dispersion, while a combination of these allows for simultaneous compensation for the second and the third orders, as described, for instance in an article by R. L. Fork, C. H. B. Cruz, P. C. Becker and C. V. Shank, entitled "Compression of optical pulses to six femtoseconds by using cubic phase compensation" published in Optics Letters, Vol. 12, p. 483 (1987). More recently, chirped dielectric mirrors, tailored to produce negative group velocity dispersion over a wide spectrum, have been described by R. Szipocs, K. Ferencz, C. H. Spielmann, and F. Krausz, in the article entitled "Chirped multilayer coating for broadband dispersion control in femtosecond lasers" which appeared in Optics Letters, Vol. 19, p. 201 (1994). Such chirped mirrors have been used to compress pulses down to durations of sub-5 fs, as described in the article entitled "Compression of high-energy laser pulses below 5 fs ." by M. Nisoli, S. De Silvestri, O. Svelto, R. Szipocs, K. Ferencz, Ch. Spielmann, S. Sartania, and F. Krausz, published in Optics Letters, Vol. 22, p. 522 (1997).
However, in cases where the pulses are uncharacterized, or when the spectral phase cannot be approximated by the leading few terms of the corresponding Taylor expansion, these techniques for pulse compression cannot be used efficiently, since the spectral transfer function needed to form the desired output pulse cannot be calculated. A specific spectral transfer function corresponds to a specific complex input pulse spectrum. Consequently, compression of arbitrary uncharacterized pulses down to the minimum time-bandwidth product cannot be accomplished by these prior art methods since the relative phases between the spectral components of the input pulses are not known.
Furthermore, practical considerations limit the use of such techniques to situations where the pulse source is substantially constant in time. Actual laser sources undergo slow variations in time, therefore severely limiting the usefulness of these techniques for the compression of ultrafast pulses. As the speed of optical communication increases, the disadvantages of currently available pulse compression technologies become more and more felt. There therefore exists a critical need for a faster, more efficient, versatile pulse compressor, capable of handling arbitrary optical pulses with durations of the order of femtoseconds.